1. Field of the Invention
This invention relates to a method for upgrading low grade cerium/fluorine-containing residues for use in lubricating oil and grease compositions, and more particularly in lubricating compositions having improved antiwear properties.
2. Description of the Prior Art
Anti-wear additives are chemicals which are added to lubricants to prevent destructive metal-to-metal contact in the lubrication of relatively moving surfaces. Plain mineral oils provide good lubrication and protection against excessive wear just as long as a film of oil is maintained between the relatively moving surfaces. This kind of lubrication, termed "hydrodynamic" is governed by the parameters of the lubricant, principally its viscosity. When the pressures or rubbing speeds between the moving surfaces increase to the point where the film of oil can be squeezed or wiped out, metal-to-metal contact begins to occur, often over a significant portion of the lubricated area. This kind of lubrication, termed "boundary lubrication"is governed largely by parameters of the contacting surfaces such as surface finish, metal shear strength and the coefficient of friction between the metals involved. Unless these parameters can be chosen to meet expected pressures and rubbing speeds, destructive metal-to-metal contact will occur. Such destructive contact manifests itself in various ways including scoring, scuffing, ridging, rippling and, in extreme cases, welding, leading to a catastrophic deformation and/or complete destruction of the lubricated component.
Anti-wear additives, which are added to many lubricants to prevent such conditions from occurring, appear to function by reacting with relatively moving surfaces under boundary lubrication conditions to form an adherent solid lubricant film which has a lower shear strength than that of the metal surfaces. It is thought that this film takes over the task of lubrication when metal-to-metal contact occurs, thus protecting the metal surfaces from damage.
Over the years, the development of satisfactory oil and grease compositions for preventing excessive wear under high pressure, high temperature and/or high speed conditions has received much attention and numerous additives have been proposed to for such service. Such additives are compounds that generally contain lead, sulfur, phosphorus, halogen (principally chlorine), and carboxylate salts, organic phosphates and phosphites. The list also includes chlorinated waxes, sulfurized unsaturated organic compounds, heavy metal sulfides such as lead sulfide and molybdenum disulfide, and antimony thioantimonate.
More recently, it has been shown by Aldorf, in U.S. Pat. No. 4,507,214, the teachings of which are incorporated herein by reference, that rare earth halides, in general and cerium trifluoride, in particular, impart both improved anti-wear and extreme-pressure capabilities to lubricating compositions, particularly at higher temperatures. However, reasonably pure cerium trifluoride is quite expensive. It would be highly desirable if more plentiful, lower grade cerium/fluorine-containing materials could be economically upgraded to a point where they would be satisfactory for use as an anti-wear additive in a lubricating composition. The present invention provides a method for so doing.